linux-kernel - Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch

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Date:   Thu, 25 Apr 2019 16:12:42 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     mingo@...hat.com, peterz@...radead.org, hpa@...or.com,
        ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        dave.hansen@...el.com, arjan@...ux.intel.com, adobriyan@...il.com,
        akpm@...ux-foundation.org, aubrey.li@...el.com,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v17 1/3] proc: add /proc/<pid>/arch_status

On 2019/4/25 15:20, Thomas Gleixner wrote:
> On Thu, 25 Apr 2019, Li, Aubrey wrote:
> 
>> On 2019/4/25 5:18, Thomas Gleixner wrote:
>>> On Mon, 22 Apr 2019, Aubrey Li wrote:
>>>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>>>> index 5ad92419be19..d5a9c5ddd453 100644
>>>> --- a/arch/x86/Kconfig
>>>> +++ b/arch/x86/Kconfig
>>>> @@ -208,6 +208,7 @@ config X86
>>>>  	select USER_STACKTRACE_SUPPORT
>>>>  	select VIRT_TO_BUS
>>>>  	select X86_FEATURE_NAMES		if PROC_FS
>>>> +	select PROC_PID_ARCH_STATUS		if PROC_FS
>>>
>>> Can you please stop mixing arch and proc code? There is no point in
>>> enabling this on x86 right away.
>>>
>>>> +
>>>> +config PROC_PID_ARCH_STATUS
>>>> +	bool "Enable /proc/<pid>/arch_status file"
>>>
>>> Why is this switchable? x86 selects it if PROC_FS is enabled and all other
>>> architectures are absolutely not interested in this.
>>
>> Above and this, I was trying to avoid an empty arch_file on other architectures.
>> In previous proposal the entry only exists on the platform with AVX512.
> 
> What's the benefit of having a conditional enabled empty file for all other
> architectures? Nothing AFAICT.
>  
>>>> +/*
>>>> + * Add support for task architecture specific output in /proc/pid/arch_status.
>>>> + * task_arch_status() must be defined in asm/processor.h
>>>> + */
>>>> +#ifdef CONFIG_PROC_PID_ARCH_STATUS
>>>> +# ifndef task_arch_status
>>>> +# define task_arch_status(m, task)
>>>> +# endif
>>>
>>> What exactly is the point of this macro mess? If an architecture selects
>>> CONFIG_PROC_PID_ARCH_STATUS then it has to provide proc_task_arch_status()
>>> and the prototype should be in include/linux/proc_fs.h.
>>
>> I was trying to address Andy's last comments. If we have the prototype in 
>> include/linux/proc_fs.h, we'll have a weak function definition in fs/proc/array.c,
>> which bloats other architectures.
>>
>> In that way proc_task_arch_status() should be defined in asm/processor.h,
>> but proc_task_arch_status() has four parameters, I don't want unnecessary
>> "struct pid_namespace *ns" and "struct pid *pid" leaked into arch headers,
>> so I defined task_arch_status(m, task) to avoid that.
> 
> This #define mess is ugly and pointless.

> Let the arch select CONFIG_PROC_PID_ARCH_STATUS 

Sorry, I didn't get the point here, above you mentioned not mixing arch and proc code
and not enabling this on x86 right away, then how to let x86 select it?

Thanks,
-Aubrey

>and if it selects it it has to provide the function. No waek function required at all.
> 
> Thanks,
> 
> 	tglx
>